Strategies for the Synthesis of Functional Naphthalene Diimides

Abstract

Naphthalene diimides, which have for a long time been in the shadow of their higher homologues the perylene diimides, currently belong to the most investigated classes of organic compounds. This is primarily due to the initial synthetic studies on core functionalization that were carried out at the beginning of the last decade, which facilitated diverse structural modifications of the naphthalene scaffold. Compounds with greatly modified optical and electronic properties that can be easily and effectively modulated by appropriate functionalization were made accessible through relatively little synthetic effort. This resulted in diverse interesting applications. The electron-deficient character of these compounds makes them highly valuable, particularly in the field of organic electronics as air-stable n-type semiconductors, while absorption bands over the whole visible spectral range through the introduction of core substituents enabled interesting photosystems and photovoltaic applications. This Review provides an overview on different approaches towards core functionalization as well as on synthetic strategies for the core expansion of naphthalene diimides that have been developed mainly in the last five years.

9H‐Quinolino[3,2,1‐k]phenothiazine: A New Electron‐Rich Fragment for Organic Electronics

“…We determined their LUMO energy levels from the onset potential of their reduction at -1.85 and -2.06 eV for SQPTZ-F and SQPTZ-TXO 2 , highlighting the stronger electron-poor character of TXO 2 compared to that of F in accordance with the above mentioned results on HOMO energies. The electrochemical gaps (∆E el ) were found to be 3.31 eV for SQPTZ-F and 3.24 eV for SQPTZ-TXO 2 . Thus, SQPTZ-TXO 2 possesses a ∆E el significantly contracted by 0.2/0.3 eV compared to that of the PA and IA counterparts (∆E el SPA-TXO 2 =3.43 eV, ∆E el SIA-TXO 2 =3.56 eV) due to its high HOMO energy level.…”

“…As TXO 2 and F moieties are oxidised through irreversible processes, these two oxidation waves have been assigned to two single electron transfers involving the QPTZ core. Thus, the first oxidation of the QPTZ fragment remarkably occurs at a less anodic potential than that of the PA (E 1 > 1.11 V in SPA-TXO 2 ) [17] and that of the IA core (E 1 =1.33 V for SIA-TXO 2 and 1.19 V for SIA-F). [14] This strong electron rich character finds hence its origin in the electron donating behaviour of the intracyclic sulphur atom, which fully drives the HOMO energy level of these dyes ( Figure 4).…”

“…[1][2][3][4] Since the discovery of the 'host/guest concept' in Phosphorescent Organic Light Emitting Diodes (PhOLEDs), [5] the design of OSCs usable as host materials for blue emitting phosphors has been an intense research field worldwide. [4] In addition to its high thermal/morphological stability and its high triplet energy (E T ), an ideal host should also possess a bipolar character with HOMO and LUMO energy levels adapted to the Fermi levels of the electrodes.…”

“…The HOMO levels are spread on the QPTZ fragment (Figure 4), confirming a first electron transfer from this core. The calculated LUMO levels are respectively lying at -0.92 and -1.17 eV for SQPTZ-F and SQPTZ-TXO 2 and are spread out on the fluorene of SQPTZ-F and on the TXO 2 of SQPTZ-TXO 2 (Figure 4). There is hence a complete electronic separation between the HOMO and the LUMO, which will have important repercussions on the photophysical processes (see below).…”

N,N′-Bis(2-cyclohexylethyl)naphtho[2,3-b:6,7-b′]dithiophene Diimides: Effects of Substituents

“…Rylene diimides, represented by naphthalene diimide (NDI, Figure 1a), have been the focus of studies in the past few decades because of their potential use in chromophores, supramolecules, optoelectronic materials, and n-type organic semiconductors [1][2][3][4]. On the one hand, the optical properties of the rylene diimide-based system can be tuned by the central rylene moiety [5,6], i.e., increasing the number of naphthalene moieties (Figure 1b) can drastically alter the absorption range from ultraviolet to visible and to the infrared region.…”